1. Field of the Invention
Broadly, the field is external heat engines, which can also be redesigned and used as heat pumps. Within this category the field is external heat engines or heat pumps comprising what might be described as a part of a centrifugal fan acting as a compressor and a second centrifugal fan operated backwards and acting as an expander. When I say fan I am actually talking about a compressor or an expander. The fan part differs from conventional centrifugal fans, because the output is directed with a substantial axial component as opposed to almost entirely tangential output for a standard centrifugal fan. The engine fans also differ from conventional fans in that when the engine is idling, the output of the fan may be zero. There is an unstable equilibrium when the fluid is merely rotating with the engine as a whole. The engine power output is associated with the circulation of the working fluid relative to the rotating engine and the velocity changes producing pressure and temperature changes due to that circulation and rotation. The rotation of the engine amplifies the effects of the circulation.
2. Description of Related Art
There are many external heat engines that expand and contract a working fluid. One of my favorites is the Stirling engine which uses a large piston to oscillate the fluid between being cooled and being heated. The oscillation is caused by sending it through a regenerator and having a heat source on one side and a cooling source on the other side of the regenerator. The power output piston is synchronized out of phase with the oscillator piston. There is friction and pressure loss at both pistons. My invention requires no piston and no chamber that changes volume. Also no regenerator, which causes power loss, is necessary.
Other engines use a compressor followed by an expander. The closest to my invention use centrifugal compressors, similar to axial compressors that push the fluid along the rotation axis of an impeller. A jet engine for example is an internal combustion engine that can use a compressor up front. Parts of the compressor move with respect to other parts of the compressor. This produces energy loss even when the engine is only idling. It also may produce loss of the working fluid. It may also cause problems when the blades move faster than the speed of sound with respect to the casing in which they reside.
My invention has essentially no working fluid loss. It also has essentially no energy loss when idling, since there are no parts moving with respect to each other, except at the rotating axle. Even the working fluid is almost not moving with respect to its container. Even when the engine is going at full speed, the only sound speed problems would be between the rotating casing and a surrounding container. When idling my engine acts like the child's toy, a rotating top. Also the engine has no moving seals contacting the working fluid, thus requiring no lubrication. The engine has no seals at all, except on the axle of the engine. It should last forever with no maintenance.
The most closely related art would be centrifugal compressors, since my invention combines two of these, but the output of each is not tangential and the output of one is at the fan area closest to the axis of rotation. Thus an expansion fan is operated like a compressor in reverse, receiving input far from the axis and expelling output very near the axis. To get a larger difference in pressure between the input and output of the compression fan, the spiral as it goes from the center to the outside is retrograde (counter to the rotation direction). Thus the normal to the surface that pushes the working fluid has a positive radial component. The larger the pressure ratio, the larger the temperature ratio can be and thus the larger the theoretical efficiency of the engine. The current limits of the compression ratio on centrifugal compressors is about ten to one. External heat will be added after the compression, when the fluid is substantially furthest from the axis of rotation.
Actually the engine does not use a purely centrifugal fan, because after the working fluid almost reaches the extreme distance from the rotation axis, for best efficiency, it must be expelled more nearly parallel to the rotation axis, so it can be directed to the second centrifugal fan, which will act as an expander producing power. The impellers may be partially twisted to accomplish the expulsion of the working fluid in a direction nearly parallel to the rotation axis. Also the fan compartment may be shaped so that the fluid first is traveling away from the other fan but at the time to exit the fan it is traveling more toward the other fan. Thus the fan is a cross between a radial fan and an axial fan and the fan compartment is warped to be more like the curved surface of a half of a sliced bagel ready for the spreading of cream cheese. Also each impeller may spiral further from the axis on the side closer to the other fan, thus allowing a radial component in the velocity as it leaves the fan. Of course there is a large tangential component in inertial space, but not relative to the working fluid container. In a conventional centrifugal fan the output fluid is usually expelled perpendicular to the rotation axis.
The heat cycle of the engine of this invention is as follows. The working fluid goes through compression, followed by adding heat, followed by expansion, followed by cooling, then repeat often. A cycle of the same description is used by other engines using a compressor and an expander. Ideally, the cycle is performed adiabatically (no heat added or subtracted from the working fluid), except at the extremes where heat is being added or removed.
Ideally the blades of the centrifugal fans meet the fluid so that the fluid is traveling in a direction parallel to the blade surface just before contact and just after leaving each blade. Each blade may be replaced by several blades at varying distances from the axis. Ideally, for maximum efficiency the pressure difference in each fan is maximized producing the largest temperature ratio possible. The extreme pressure ratio on centrifugal compressors is currently about 10:1. At ratios above ten the compressor may wear out fast and may be dangerous. A ratio of 5:1 would be adequate for very good efficiency and reduced risk and reduced energy loss within the engine. Other reasons to reduce the pressure ratio will be discussed later.
One object of the current invention was to produce an engine/heat pump which, when operating at a steady speed, has no changes in temperature at any particular point. Thus heat loss due to changing operating temperatures at a particular position are negligible. Heat loss due to conduction along the parts with spatial temperature differences can be minimized in several ways. Heat transfer by conduction along the blades could be minimized by using ceramic blades, or by replacing long blades with a series of blades occurring at varying distances from the rotation axis. Heat transfer in the area between the hot and cold heat exchangers can be minimized by using ceramic or by using insulating lining on the parts closer to the axis of rotation (the cold heat exchanger area) where centrifugal forces are lower. The insulating lining would be forced toward the body being lined by centrifugal forces. Any insulating layer would not be subject to friction wear, since neither the fan blades nor any other parts of the engine touching the working fluid move relative to each other, except for minor adjustments of the blade angle with respect to fluid flow.
Another object was to produce an engine where there is essentially no loss of pressure around pistons or blades. Prior engines would produce localized circulations and turbulence especially where the blades are close to the blade casing. There is rapid relative motion between closely spaced components in most prior art. In my invention the casing which is touched by the working fluid moves with the same rotation rate as the blades, so the blades do not move with respect to the casing, except for angle adjustments.
Another object of the current invention is to produce an engine comprising a centrifugal compressor and a reverse operated compressor in which the working fluid speeds above Mach 1.3 in the compressor are not a problem, because that speed is actually only relative to the outside of the engine. The speed of the working fluid relative to the blades and to the casing used to contain the working fluid is much smaller. The only high relative speeds are between the working fluid container and the flow container for the external fluid in the hot flow heat exchanger. The fluid between the two fast moving surfaces will be near atmospheric pressure and will take on the average speed, being much lower than Mach 1.3. If the heat input is concentrated sunlight, then there does not need to be a flow container for the external fluid although a glass container might be used to prevent heat loss to the atmosphere. The light could be directed onto the working fluid container.
Another object of the invention was to produce an engine with negligible friction loss, since there are no solid parts moving relative to each other due to the engine cycle. Of course, as with most engines, the output shaft is rotating with respect to the device propelled by the engine.
Another object of the invention was to produce an engine that would have no loss of working fluid to the outside or around pistons, since substantially the working fluid is in a container that does not necessarily change shape or volume, except for stress or strain. Argon gas would not permeate or escape from its enclosure if steel is used.
Another object is to produce an engine wherein the working fluid can be at a much higher pressure internally, where the relative motion with respect to the container is small, and wherein the relative motion of the container with respect to the atmosphere can be much larger.
Another object of the current invention was to produce an engine which produces very little metal fatigue, since the parts do not move relative to each other during operation.